Method



I April 16,- 19'46. F, w. CRAWFORD METHOD OF PROSPECTING FOR HYDROCARBONS Filed June 17, 1940 4 shets-sheei 1 INVENTOR FRANCIS W.CRAWFORD ATT April 16, 1946; F. w, CRAWFORD METHOD OF PROSPECTING FORRHYDROCARBONS Filed June l7, 1940 4 Sheets-Sheet 2 Puma Z IhlmO O 20 OIL SATURATION OF CORE PERCENT o 200 HYDROCARBONS-cumc MM/ IOGM. MUD

DDYE n. E E D Em... DL L 5 L m M m M m m mm s S MS 5 S UB5 0 0 0 0 c c c B O 2 4 6 B O 3 4 4 4 4 4 5 kuum Z Ihmuo FIG. 2

INVENTOR FRANCIS W. CRAWFORD .I .BY

Patented Apr. 16, 1946 METHOD, OF PBOSPECTING FOR HYDBOCARBONS Francis W. Crawford, Bartlesvllle, kla., assignor to Phillips Petroleum Company, a corporatlon of Delaware Application June 17, 1940, Serial No. 341,047 3 Claims. (01. 23-232) sufllciently sensitive technique will reveal the ap- This invention relates to a method of extracting hydrocarbons from earth samples or drilling mud.

The invention is based on the experimental fact that formations in or near petroleum bearing zones contain hydrocarbons and in extremely small amounts and that in general the hydrocarbon concentration is some inverse function of the distance of the formation from the petroleum.

In practice, when applied to the drilling of a well, the procedure is to obtain and analyze samples of drilling mud or formation cuttings at spaced intervals of the depth during the drilling of a bore hole or well. A log of the well can then be made by plotting a graph of the hydrocarbon content of the samples versus the depths from which the samples came. If formation cuttings are used it involves collecting samples separated from the discharge drilling mud stream by ashale shaker or similar screening device or a sample of the mud stream itself before it passes through the screening device may be collected and used. In this latter case the combined cuttings anddrilling fluid are subjected to the analysis. If drilling mud is used, then samples from both the input and discharge streams are preferably secured and analyzed, and the results plotted in the form of a well log. Differences between the logs obtained from the two mud streams are significant.

The analyses of soil samples, that is, near surface formation samples, deeper formation cuttings or drilling mud are made for total hydrocarbon content or for one or more individual hydrocarbon fractions, 1. e. methane, ethane, propane, etc., as may be desirable or possible in any particular case.

There are several interesting aspects to the information to be obtained by knowing the hydrocarbon content of the soil, formation cuttings or drilling mud either as a continuous function of the depth of the drill hole or at a number 'of closely spaced points over the entire depth of a well, In areas where deep production is expected, shallow sands are sometimes passed without receiving much attention and analysis of drilling mud or formation cuttings gives additional information concerning them at small expense. Also, there is the important situation that in this way one can detect the presence of gas or oil bearing formations that might ordinarily be mudded ofi unknowingly. Finally, the formations immediately above oil and/or gas reservoirs have rapidly increasing hydrocarbon content and a proach to the saturated horizon some distance in advance of the drill. I

The demands made on any extraction process for removing hydrocarbons from soils, formation cuttings or drilling muds are (1) that it yield results reproducible within the estimated experimental errors of analysis, (2) that it be simple and economical and (3) that it extract adsorbed and absorbed hydrocarbons as well as dissolved hydrocarbons. The process and apparatus disclosed here have been found to fulfill these requirements.

It is therefore a principalobject of this invention to extract hydrocarbons from earth samples or drilling mud which is employed in the course of drilling a well bore.

The present invention has for another object the provision of a method adapted to extract hydrocarbons from earth samples or drilling mud in an effective and relatively economical manner.

Figure 1 is a view partly in elevation and partly in vertical section of apparatus embodying the invention.

Figures 2 to 4 inclusive are graphs showing results of actual tests in accordance with the present invention.

In itsessentials the method of extracting hydrocarbons from drilling mud, soil, or formation trolled heat under a low absolute pressure. An apparatus which has been developed to do this for routine analysis is shown in detail in Figure 1, and forms a part of the present invention.

In Figure 1 reference numeral I'll indicates a copper jar hermetically sealed by brass plate II and gasket I! held in place by compression ring l3. Jar I0 is surrounded by an insulating jacket H which has embedded therein a thermostat IS in contact with jar l0 At its lower end jar I0 is in heat conducting relation with an electric heater [6 controlled by thermostat 15. A source of electric power, not shown, is connected to the heater. All permanent joints in jar III are sealed with silver solder. Plate I I has an opening therethrough carrying a nipple I! which is connected through a T l8 to an airintake pipe I!) having interposed therein a needlevalve 20. The leg of T I8 is connected to a ball condenser 2| by means of a pipe 22 having a gate valve 23 interposed therein. Ball condenser ii is supported on a pedestal 24 which has direct connection Wlbhs the ball condenser through a T 25 and a nipple 26. The leg of T 25 connectswith a drain pipe 2| having a needle valve 34 interposed therein.

At its upper extremity ball condenser 2| makes connection with a T 29 through nipple 28. A vacuum gauge 30 is connected to one leg of 'l' 29 and a pipe 3| having a needle valve 82 interposed therein is connected to the other leg of T 29. Cold water tubes 33 surround ball condenser 2| in heat exchanging relation with its outer surface. y

In operation an earth or drilling mud sample to be tested is placed in jar l and the Jar sealed.

The air is quickly pumped from the apparatus to produce a vacuum in jar Hi. It is recommended that this step in theprocedure be carried out by means of a suitable vacuum pump (not shown) connected to pipe 3|, with valves 20 and 34 closed and with valves 23 and 32 in open position. It will be obvious, however, that a vacuum may be produced in jar l0 by connecting a vacuum pump to pipe I 9 and operating the same with valve 20 open and valve 23 closed or by connecting such a pump to pipe 21 and opening and closing the necessary valves to permit of desired evacuation of said jar. Assuming that the pump is connected to pipe 3|, as recommended above, it will be seen that ball condenser 2| will be evacuated at the same time I and to the same extent as. jar Hi. When the desired vacuum of about 0.1 atmosphere is relatively rapidly obtained in jar l0, gate valve 23 is closed to protect the sample from undue. loss of sorbed hydrocarbons during the relative long time necessary to reduce the pressure in large condenser 2| as low as possible and condenser 2| is then preferably further evacuated, the vacuum to be attained in condenser 2| being limited primarily by vapor pressure at room temperature of any residual water that may collect therein. The volume ratio of 21 to is such that when 2| has been almost completely evacuated of air and 23' is opened the air at 0.1 atmosphere in H1 will difier uniformly in 2| and I0 giving a uniform pressure suiliciently low for effective desorption. Thus by evacuating 2| lower than I0 hydrocarbons which are slowly desorbed at room temperature under low pressure aresubstantially conserved to the system for measurement. Valve 32 is now closed and gate valve 23 is fully opened. Heater I6 is then placed in service and the sample in jar I0 is heated, all gases and vapors evolved therefrom being confined to jar l0 and condenser 2|. Cold water is circulated continuously through tubes 33, which, as indicated above, are in heat exchange relation with condenser 2|, in order that water distilled off from the sample may be condensed and collected' in element 2|. Water that is condensed and collected during a run is removed by way of drain pipe 27. For best results, it is advisable not to withdraw the water from condenser 2| until the method of the present invention has been carried out to completion, lest valuable material be inadvertently removed from the system. It is highly desirable to thoroughly dry the sample because only then will the temperature rise high enough in the vacuum for eifective desorption. The temperature of the sample remains in the vicinity of 135 F. until the sample is dry, then rises to a maximum of approximately 300 F. at which temperature the thermostat cuts ofi the heat. The temperature is maintained at about 250 to 300 F. until sufiicient time has elapsed that the entire sample is thoroughly dry. This time will depend upon the sample used but times of /2 to 2 hours are usually adequate. Hydrocarbon-free air is then added to the evolved vapors in the extractor by opening valve 20. The mixture of hydrocarbons and air thus obtained is passed through pipe 3|, and if desired, through a previously evacuated scrubbing tower (not shown), from whence it is admitted into the analytical apparatus. The air introduced into the system serves as a vehicle for transporting the evolved hydrocarbons and supplies necessary oxygen to support combustion as required during the analysis.

The analytical operations, disclosed in pending patent application Serial No. 297,3'19, will be described briefly. The sequence of events is as 16 follows: The gas sample is first passed through densed out.

potassium hydroxide and phosphorous pentoxide to remove carbon dioxide and water. As it flows on through a condenser cooled by liquid nitrogen all hydrocarbons except methane are con- The methane and air mixture is burned in a combustion cell and the Water of combustion removed by phosphorus pentoxide. The carbon dioxide from the combustion is then trapped in a condenser cooled by liquid nitrogen 'while the remainder of the air is pumped oil. When the requisite sample has flowed through the apparatus thercondensers are pumped to a high vacuum. The condensers are then isolated, warmed to room temperature and the pressures of the trapped components measured by means tion, a second run can so and the presence of gas or oil of an extremely sensitive pressure gauge. These two pressures determine the carbon dioxide from the combustion of methane and the total heavy hydrocarbons (C2, The condenser containing the heavy fraction is now cooled with hqurd oxygen and pumped for a few minutes to distill oil the ethane. The remaining hydrocarbons are determined by measuring their pressure at room temperature as before. The quantity of ethane is then found by subtraction. If it is desired to know more about the heavy fracbe made permitting all combustion cell and colcarbon dioxide.

the sample to enter the lecting the resultant thus obtained the total number of carbon atoms present and using the data from the previous run, the average .carbon content per molecule of heavy fraction can be computed.

As one example, in as well X, the drilling mud, composed of fresh water and well cuttings only, was sampled at approximately 10 foot depth intervals. Figure 2 presents the hydrocarbon log, core 10g, and core saturation in proper correlation as to depth.

In a log of the hydrocarbon content of drilling mud it is possible to see several interesting features. For example, in Figures 2 and 4 the correlation between either curve for discharged mud sands is lackin in detail but the curves for the input and discharged muds separate sharply when a sand is penetrated and then converge when the sand has been passed. This indicates that when an oil or gas sand is being drilled the discharged mud picks up hydrocarbons but that much of the hydrocarbon remains in the mud and thus the total hydrocarbon content of the mud in the pit builds up and tends to remain at a new tent would continueto increase instead of rea certain well, designated maim'ng approximately constant down to the next oil or gas horizon,

Th'e hydrocarbon log shown in Figure 3 was made with less detail of sampling than the one in Figure 2 but it covers several formations having showings of oil or gas.

In Figure 4 the hydrocarbon log of a well is plotted together with the lithological log, drilling time chart, and oil saturation.

For this log all the hydrocarbons extracted from the mud were burned at one operation and the resulting CO2 values plotted. A more complete analysis gives useful information concerning the composition of the reservoir hydrocarbons, for example, whether the gases encountered are principally methane or a mixture of hydrocarbons.

The solid line graph on the hydrocarbon log,

Figure 4, traces the gas content of the discharge mud while the dashed line is for the suction mud. There are several zones in which these curves diverge considerably and thus indicate the presence of hydrocarbon bearing formations. They are 2950 to 2980, 3010 to 3040, 3050 to 3100 and 3110 to 3165. Other data, such as are obtained from the sample log, drilling time and core anal-. ysis, are used to localize and further evaluate the possible producing horizons.

Recalling that low points in the drilling time log indicate soft formations. it is interesting to correlate the same or lithogical log, hydrocarbon log and drilling time log. For example at 2870 there is a soft streak but neither the sample 10g nor hydrocarbon log show the presence of oil or gas, whereas at 2970-80 there are distinct breaks in both the hydrocarbon log and drilling time log. The hydrocarbon log begins to increase at 2960 which is some 10 feet above this soft zone indicated by the drilling time log. The sample log shows saturation at the uncorrected depth of 2980 which upon correction becomes about 2970 for an accurate check.

In one series of experiments lubricating compound used on drill pipe joints was placed in the extractor in concentrations of 25 per cent compound to 75 per cent water in order to determine the effect of this known contamination in the drilling mud. The analytical results were about per cent of the readings obtained on mud samples from the saturated horizons in well X.

In view of the exaggerated quantity oi contami- I claim:

1. The method of analyzing a sample of drilling mud for hydrocarbons, which comprises placing the sample in an isolated heating zone, rapidly evacuating the readily releasable gases and vapors from the same and separating the vapors and gases thus released from the process, evacuating an isolated condensing zone, establishing communication between the condensing zone and the heating zone, applying heat tothe sample in the heating zone, removing heat from the vapor ous eilluents of the sample in the condensing zone to condense readily condensible vapors, and analyzing the uncondensed eflluents for hydrocarbon content.

2. The method of analyzing a sample of drilling mud for hydrocarbons, which comprises placing the sample in an isolated heating zone, rapidly evacuating the readily releasable gases and vapors from the same and separating the vapors and gases thus released from the process, evacuating an isolated condensing zone, establishing communication between the heating zone and the condensing zone, applying heat to the sample in the heating zone to evolve volatile and adsorbed components therefrom, removing heat from the vaporous eflluents of the sample in the condensing zone whereby water vapor is condensed, admixing air with the uncondensed effluents of the sample, and analyzing the resulting mixture for hydrocarbons by combustion.

3. The method of analyzing a sample of drilling mud for hydrocarbons, which comprises isolating the sample in a heating zone, evacuating a condensing zone to low subatmospheric pressure, establishing communication between the condensing zone and the heating zone whereby the pressure of the heating zone is reduced, aplying heat to the sample in the heating zone for vaporization of the water therefrom and removing heat from the vaporous efiluents of the sample in the condensing zone to condense the water vapors and maintain the reduced pressure in the heating zone until water vapors cease to 7 vaporize in the heating zone, subsequently elevating the temperature of the sample above the boiling point of water and below the temperature at which organic constituents of the sample decompose to form hydrocarbons by further heating, and analyzing the uncondensed eiiluents of the sample for hydrocarbon content.

FRANCIS W. CRAWFORD. 

